Java ExecutorService如何实现任务优先级

在Java中，ExecutorService本身并不直接支持任务的优先级。但是，你可以通过使用PriorityBlockingQueue和自定义的ThreadFactory来实现任务优先级。

以下是一个简单的示例，展示了如何使用PriorityBlockingQueue和自定义的ThreadFactory实现任务优先级：

1. 首先，创建一个实现了Runnable接口的任务类，并在其中添加一个priority字段来表示任务的优先级。

public class PriorityTask implements Runnable, Comparable<PriorityTask> {
    private int priority;
    private Runnable task;

    public PriorityTask(int priority, Runnable task) {
        this.priority = priority;
        this.task = task;
    }

    public int getPriority() {
        return priority;
    }

    @Override
    public void run() {
        task.run();
    }

    @Override
    public int compareTo(PriorityTask other) {
        return Integer.compare(other.priority, this.priority);
    }
}

2. 创建一个自定义的ThreadFactory，用于创建具有优先级的线程。

import java.util.concurrent.ThreadFactory;

public class PriorityThreadFactory implements ThreadFactory {
    private int counter = 0;

    @Override
    public Thread newThread(Runnable r) {
        Thread t = new Thread(r, "PriorityThread-" + counter++);
        t.setDaemon(false);
        t.setPriority(Thread.NORM_PRIORITY);
        return t;
    }
}

3. 创建一个ExecutorService，使用PriorityBlockingQueue作为任务队列，并使用自定义的ThreadFactory创建线程。

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.PriorityBlockingQueue;

public class PriorityExecutorService {
    public static void main(String[] args) {
        PriorityBlockingQueue<Runnable> queue = new PriorityBlockingQueue<>();
        ExecutorService executorService = new Executors.newFixedThreadPool(5, new PriorityThreadFactory());

        executorService.submit(new PriorityTask(3, () -> System.out.println("Task 3")));
        executorService.submit(new PriorityTask(1, () -> System.out.println("Task 1")));
        executorService.submit(new PriorityTask(2, () -> System.out.println("Task 2")));

        executorService.shutdown();
    }
}

在这个示例中，我们创建了一个PriorityExecutorService类，它使用PriorityBlockingQueue作为任务队列，并使用自定义的PriorityThreadFactory创建线程。我们提交了三个具有不同优先级的任务。当你运行这个程序时，你会看到任务按照优先级顺序执行。